1. Field of the Invention
The present invention relates to a novel dichroic azo dyestuff used for a polarizing film and the polarizing film thereof.
2. Description of the Related Art
The current polarizing films are grouped into Ioding Type and Dye Type.
Ioding Type Polarizing Film: the polarizing film constituted with PVA and iodine is the major part of the market. The major disadvantage of Ioding Type Polarizing Film is that the polarized efficiency is reduced within the elapsed time under high temperature and moisture. Although the utilization of boric acid, glyoxal, or heat treatment which can form polyethylene caused by the reduction of OH groups enhances the heat proof character, it is still not met the requirement of heat and moisture proof claimed in some situations.
A direct azo-dye is the major part of the dichroic dyestuff used for Dye Type Polarizing Film. It is the characteristic that the axial in the structure of the dye molecule is linear. Thereby, the dichroic property is presented due to the difference between the absorbance of the molecule with the parallel and perpendicular axial to light.
Dye Type Polarizing Film: a dye type polarizing film, with preferred heat proof, moisture proof and so on, is usually used for the outdoor type displays necessary for cars, airplanes and so on. However, the major disadvantage is the low polarized efficiency. The manufacturing method, through the stretching alignment of PVA and the dyes with identical absorbance and high-polarized efficiency in visible light, is the same as that of Ioding Type Polarizing Film. Generally, the direct dyes or acid dyes with azo groups are used. As compared with Ioding Type, Dye Type has preferred heat and moisture stability. In other words, it has preferred heat and moisture proof.
The present invention displays that the derivation from the core structure of the azoxy type polarizing film to establish side chains can provide high-polarized efficiency and climate proof. The purity of the easily afforded dyestuff by less synthetic steps is preferred, without complicated purification. The PVA type polarizing film of the dyestuff has preferred heat and moisture proof and its polarized efficiency is equal to that of Ioding Type Polarizing Film.